Corrosion resistance and degradation behavior of anodized Mg-Gd alloys: A comparative study

A conventional anodic oxidation process was conducted on two Mg-Gd alloys to study the corrosion resistances and degradation behaviors of their anodized films, and a commercial AZ31 alloy was used for comparison. It was found that both the structures and degradation properties of the anodized films of Mg-Gd alloys were quite different from AZ31 alloy. For Mg-Gd alloys, the anodized films contained more crystalline MgO, Mg2SiO4 and Mg3(PO4)2 with lower porosity and small pore size compared with anodized AZ31 alloy. Although the anodized AZ31 alloy showed slightly higher initial corrosion resistance, its long-term degradation performance was uncompetitive compared with two anodized Mg-Gd alloys. And the scanning electrochemical microscopy (SECM) tests also pointed to more uniform degradation behaviors of anodized Mg-Gd alloys. The better long-term degradation performances of anodized Mg-Gd alloys, especially anodized Mg-1Zn-1Gd alloy, were believed to benefit from their different structures, compositions and corrosion products of anodized films compared with anodized AZ31 alloy.